Mirëdor seems to be a corrupt form of the Quenya name Mîrënóre, maybe a topographical name scholars of the Elendili used in old maps.It seems highly unlikely that the name was ever used or even known in the utter south due to the animosity of the Kingsmen for use of the elven tongues.Zimrathâni however is the correct translation of Jewel-Land into Adûnaic.